Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.68   8.359%   $225.04   $225.04   $225.05   $225.00  
  Purchase #2 $50.42   4.437%   $52.6571   $52.66   $52.65   $52.70  
  Purchase #3 $158.75   11.692%   $177.3111   $177.31   $177.30   $177.30  
  Purchase #4 $32.80   4.715%   $34.3465   $34.35   $34.35   $34.30  
  Purchase #5 $202.72   13.847%   $230.7906   $230.79   $230.80   $230.80  
  Purchase #6 $188.68   6.364%   $200.6876   $200.69   $200.70   $200.70  
  Purchase #7 $119.84   13.772%   $136.3444   $136.34   $136.35   $136.30  
  7 purchase totals = $960.89       $1,057.1773   $1,057.18   $1,057.20   $1,057.10